In automobile engines, in order to cool these, typically a cooling system of the water-cooling type using a radiator is employed. Conventionally, in a cooling system of this type, a thermostat or the like, employing a thermally expansive body whereby the flow rate of cooling water circulated to the radiator was adjusted, was employed in order to control the temperature of the cooling water that was introduced into the engine.
Specifically, a control valve such as a thermostat employing a thermally expansive body as described above is inserted in part of the cooling water passage, such as for example at the inlet or outlet of the engine, and, if the cooling water temperature is low, this control valve is closed so that the cooling water is circulated through a bypass passage without passing through the radiator and, if the cooling water temperature is high, the control valve is opened, so that the cooling water is circulated through the radiator: in this way, the temperature of the engine cooling water can be controlled to a desired condition.
In a conventional thermostat device of this type, there are provided a thermoelement in which is sealed a thermally expansive body that is operated in response to temperature change of the fluid and a main body frame that holds this; first and second valve bodies that respectively present substantially umbrella shapes are provided at both ends of the thermoelement. This thermoelement comprises a rod that is advanced and retracted by means of an expanding/contracting thermally expansive body that is used to sense the temperature of the fluid and is arranged such that the aforesaid valve body opens/closes a fluid passage in a manner that is linked to the movement of this rod (see for example patent reference 1).
[Patent reference 1] Japanese Patent No. 3225386